1. Field of the Invention
This invention relates generally to overvoltage protection (OVP) circuits for switching power supplies, and more particularly to OVP circuits for multiple parallel-connected switching power supplies.
2. Description of the Related Art
Some power systems employ multiple switching power supplies, the outputs of which are connected to a common bus. Such an arrangement may be used to provide a larger power output through current sharing, or to maintain the availability of the bus voltage in the event that one or more of the contributing power supplies fails. Generally, an OR-ing circuit is used to protect against power flow into each power supply from other power supplies; this ensures that power flows only out of each power supply and that the power supplies can be hot-swapped.
To improve the overall efficiency of such power systems and to reduce the overall cost, it is becoming popular to connect the power supplies directly to the common bus without the use of an OR-ing circuit. An example of such an arrangement is shown in FIG. 1. The power supplies (10, 12, 14) receive a common DC voltage at respective inputs and produce respective output voltages which are connected together to provide the system's output voltage Vo at common voltage bus 15. Overvoltage protection (OVP) circuits (16, 18) would typically be arranged to receive the common bus voltage at respective inputs (20, 22) and to provide one or more control signals (24, 26) to a respective power supply which are arranged to disable the power supply if the bus voltage exceeds a predetermined limit.
However, with no OR-ing circuits, an overvoltage condition due to one faulty power supply raises the common bus voltage, which may trigger the activation of the OVP circuits of the other power supplies connected to the bus. This may result in all of the power supplies becoming disabled, and the common bus to fail.